The Tunguska event was a powerful explosion equal to 3 to 50 million tons of TNT that happened near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of June 30, 1908 (Old Style June 17).
The explosion occurred in the sparsely populated East Siberian taiga and knocked down trees over an area of 2,150 square kilometers (830 square miles) of forest. Some eyewitnesses reported that up to three people may have died. Scientists believe the explosion was caused by a meteor exploding in the air above the Earth, which happened when a rocky asteroid about 50 to 60 meters (160 to 200 feet) wide entered Earth’s atmosphere.
The asteroid came from the east-southeast and moved at a very high speed, about 27 kilometers per second (98,004 kilometers per hour, or Mach 80). Although the event is called an impact event, the object likely exploded in the atmosphere at an altitude of 5 to 10 kilometers (3 to 6 miles) instead of hitting Earth’s surface, which is why no impact crater was found.
The Tunguska event is the largest recorded impact event on Earth in history. However, scientists believe much larger impacts happened before humans recorded them, such as the Chicxulub impact that ended the Cretaceous period. An explosion of the same size as Tunguska could destroy a large city. The event has been described in many fictional stories. On the Torino scale, which rates the risk of asteroid impacts, the Tunguska event would have a rating of 8, meaning there was a definite risk of the object hitting Earth and causing local damage.
Description
On June 30, 1908 (Old Style June 17), at about 7:17 a.m. local time (UTC+07:00), Evenki people and Russian settlers in the hills northwest of Lake Baikal saw a bright blue light moving across the sky, leaving a thin trail. Closer to the horizon, there was a flash followed by a cloud and a pillar of fire that cast a red glow. The pillar split into two and turned black. About 10 minutes later, a sound like artillery fire was heard. People near the explosion said the sound seemed to move from the east to the north. The sound was accompanied by a shock wave that knocked people down and broke windows hundreds of kilometers away.
The explosion was recorded by seismic stations across Eurasia. Air vibrations from the blast were detected in Germany, Denmark, Croatia, the United Kingdom, Batavia (now Indonesia), and Washington, D.C. Scientists believe the shock wave was as strong as an earthquake measuring 5.0 on the Richter scale in some places.
In the days after the event, night skies in Asia and Europe glowed brightly. Photographs taken at midnight in Sweden and Scotland showed unusual brightness without flashbulbs. Scientists think this happened because light passed through ice particles high in the atmosphere, created by the explosion’s extreme cold. This effect was later seen in smaller amounts during space shuttle missions. In the United States, scientists at Mount Wilson Observatory noticed a long-term decrease in atmospheric clarity, suggesting more dust particles were in the air.
Although the Siberian area where the explosion happened was sparsely populated in 1908, eyewitnesses and local newspapers reported the event soon after.
Testimony of S. Semenov, recorded by Russian mineralogist Leonid Kulik’s expedition in 1930:
At breakfast time, I was sitting by the house at Vanavara Trading Post, facing north. Suddenly, I saw the sky split in two, and fire appeared over the forest. The split grew larger, and the northern side was covered in fire. I felt intense heat, as if my shirt was burning. Then the sky closed, and a loud thump knocked me several meters. I lost consciousness briefly, but my wife helped me back to the house. Later, I heard loud noises like falling rocks or cannons, and the ground shook. Hot wind blew between houses, leaving marks in the ground and damaging crops. Later, we saw broken windows and a broken iron lock in the barn.
Testimony of Chuchan of the Shanyagir tribe, recorded by I. M. Suslov in 1926:
We were sleeping in a hut with my brother Chekaren when we suddenly woke up. Someone pushed us, and we heard whistling and felt strong wind. Chekaren said, “Can you hear birds flying overhead?” We couldn’t see outside. Then I was pushed again and fell into a fire. We cried for our family but got no answer. We heard trees falling and ran outside, but thunder struck. The ground shook, and wind knocked our hut down. I saw trees falling and branches on fire, as bright as a second sun. Then came a loud thunderclap. Later, we saw another flash and heard more thunder. The wind knocked us down again, and we watched trees snap and burn. Chekaren pointed to another flash, and we heard more thunder. The final thunder was far away, like the sun setting.
Sibir newspaper, July 2, 1908:
On the morning of June 17, around 9:00 a.m. (UTC+7), an unusual event was observed. In the village of Karelinski, farmers saw a bright blue-white object in the northwest, moving downward for 10 minutes. The object looked like a cylinder. As it neared the ground, it turned into a large cloud of black smoke, and a loud noise like falling stones or artillery fire was heard. Buildings shook, and flames appeared. Villagers panicked, thinking the world was ending. The writer of this report was in the forest and heard artillery fire repeated every 15 minutes at least 10 times. In Kirensk, windows in buildings facing northeast shook.
Siberian Life newspaper, July 27, 1908:
When the meteorite fell, strong ground tremors were felt. Near Lovat village, two loud explosions were heard, like large-caliber artillery.
Krasnoyaretz newspaper, July 13, 1908:
In Kezhemskoye village, on June 17, an unusual event occurred. At 7:43 a.m., a loud wind was heard, followed by a terrifying thump and an earthquake that shook buildings as if hit by a heavy log or rock. Three thumps were heard, followed by an underground sound like a railway with many trains. Then, for 5 to 6 minutes, sounds like artillery fire were heard: 50 to 60 shots in quick, equal intervals, growing weaker. After 1.5–2 minutes, six more thumps were heard, like cannon fire, but individual and loud. The sky appeared clear with no clouds or wind.
Scientific investigation
Since the 1908 event, about 1,000 scientific articles (mostly in Russian) have been written about the Tunguska explosion. Because the area was very remote and scientists had few tools to study the event at the time, modern scientists have relied mostly on damage reports and geological research done many years later. Scientists estimate the explosion’s energy was between 3 and 30 megatons of TNT (13 to 126 petajoules).
No scientific study of the area happened for more than a decade after the event, partly because the region was isolated and Russia faced political changes in the 1910s. In 1921, a Russian scientist named Leonid Kulik led a team to the Podkamennaya Tunguska River basin for the Soviet Academy of Sciences. Although they did not reach the center of the blast, local stories led Kulik to believe a large meteorite caused the event. He convinced the Soviet government to fund another trip to search for meteorite material.
Kulik led another expedition to the Tunguska site in 1927. He hired local Evenki hunters to guide his team to the blast center, where they expected to find a crater. Instead, they found a burned area about 8 kilometers (5 miles) wide where trees stood upright but had no branches. Trees farther away were knocked down in a pattern radiating outward from the center.
In the 1960s, scientists measured the flattened forest area as covering 2,150 square kilometers (830 square miles), shaped like a large butterfly with a wingspan of 70 kilometers (43 miles) and a body length of 55 kilometers (34 miles). Kulik found holes he thought were meteorite craters, but he could not dig them to confirm.
Over the next 10 years, Kulik led three more expeditions. He found small, round bogs he thought might be craters. After draining one called "Suslov’s crater," he found a tree stump, proving it was not a meteorite crater. In 1938, Kulik arranged for aerial photos of the area. The original photos were destroyed in 1975, but copies were saved for study.
Expeditions in the 1950s and 1960s found tiny silicate and magnetite spheres in soil samples. Later, scientists found these spheres in tree resin. Chemical tests showed the spheres had high nickel levels, like those in meteorites, suggesting they came from space. The distribution of these spheres matched what would happen if a meteor exploded in the air.
Chemical studies of peat bogs in the area found unusual carbon, hydrogen, and nitrogen patterns. These patterns matched those found in meteorite impacts. The bogs also had high levels of iridium, similar to layers found in ancient Earth history. Scientists believe this iridium came from the meteor.
Some scientists disagree about these findings. Others say tests in different labs did not confirm the results.
John Anfinogenov suggested a rock called "John’s stone" might be a meteorite piece. However, tests showed it likely formed from hot water, not a meteor.
In 2013, researchers found fragments in a peat bog that may be from space.
Some claim the explosion knocked down over 80 million trees, but this number is likely wrong. Scientists think the actual number is smaller. The largest trees found were about 44 centimeters (17 inches) in diameter, not the 1 meter (3.3 feet) some sources claim.
Studies of atmospheric transparency at Mount Wilson Observatory suggest the explosion released about a million tons of dust into the stratosphere. Models also show the meteor may have created up to 30 megatons of nitric oxide, causing temporary ozone layer damage and increased UV-B light at certain latitudes.
The most widely accepted theory is that the explosion was caused by a meteor exploding in Earth’s atmosphere 6–10 kilometers (4–6 miles) above the ground. Meteoroids enter Earth’s atmosphere daily, moving at least 11 kilometers per second (40,000 km/h; 25,000 mph). Most burn up before hitting Earth. Early estimates of the Tunguska explosion’s energy ranged from 10–15 to 30 megatons of TNT.
Recent studies suggest the energy was between 3–5 megatons. This is about 1,000 times the energy of the Trinity nuclear test and similar to the Castle Bravo test in 1954. A 2019 study estimated the explosion’s power was about 20–30 megatons.
Since the late 20th century, scientists have used infrasound and satellite data to monitor Earth’s atmosphere, helping track asteroid air bursts.
Similar event
On February 15, 2013, a smaller explosion in the air happened over a populated area in Chelyabinsk, a city in the Ural region of Russia. The object that caused the explosion was an asteroid, which was about 17–20 meters (56–66 feet) wide. It had an estimated weight of 11,000 tonnes and released energy equal to about 500 kilotons. The explosion caused over 1,200 injuries, mostly from broken glass that fell when windows were shattered by the powerful wave of energy from the event.
Aftermath
In fiction, many different ideas about what caused the event are presented. One common idea is that it was caused by an alien spaceship. This idea became popular after Russian science fiction writer Alexander Kazantsev published his 1946 short story titled "Explosion."
In 2016, the United Nations declared June 30 as the annual International Asteroid Day. This day is meant to increase understanding about asteroids and the work being done to protect Earth from potential asteroid impacts.